Transmission line



Dec. 29, 1942. G. 1.. USSELMAN 2,306,850

TRANSMISSION LINE Filed May 3, 1940 70 ANTENNA vi 1 ix 9) :& 9) 11 HEAT f" EXCHANGE/2 I .1 I I T0 POWER %5/ su mv 6/ -ro TRANSMITTERVT W050 AUDIO INSUI A TING TUBE WATER IN 33 30 p p HEAT sxcmuasn 34 WATER our INVENTOR GEORGE L. USSELMAN A TTORNEY.

Patented Dec. 29, 1942 UNITED STATES PATENT OFFICE TRANSMISSION IJINE 3 of Delaware Application May 3, 1940, Serial'No.'333,117

4 Claims.

The present invention relates to coaxial trans-' mission lines and, more particularly, to a means for cooling high power coaxial transmission lines.

With the recent continuous and substantial increase in power and in operating frequencies the problem of heat dissipation has become very important. Although the power loss'per unit length in coaxial transmission lines is comparatively small, the inner conductor of the line cannot rid itself of heat very readily. At any rate, its heat radiating capabilities are very much smaller than those of the outer conductor. Consequent-- 1y, the:inner conductor of the coaxial transmission line when carrying high power tends to become dangerously hot. cause rapid oxidation of'the conductor and, in

extreme cases, the heat might even melt thesolder in the joints in the inner conductor. Oxidation of. the adjacent surfaces of the coaxial conductors is undesirable since the oxides of most metals have a higher resistancethan the metal itself. Since practically all of the current carriedby. the vooaxialtransmission line is carried by the adjacent surfaces, the losses in the line are increased excessively thus further increasing the heat which must be dissipated. Furthermore, due to the heating effect of the inner conductor the atmosphere within the coaxial transmission line is heated and it is well known that hot air ionizes more easily than cooler air. The heated ionized air becomes a poor insulator and thus tends to cause flash-over within the transmission line and consequent breakdown.

The present invention is directed especially toward a means of cooling coaxial transmission lines.

An object of the present invention is to efficiently remove heat from the inner conductor of coaxial transmission lines.

Still a further object of the present invention is to provide a structure for causing circulation of a cooling fluid in the space between the inner and outer conductors of a system of coaxial transmission lines.

In accordance with the present invention I propose to so connect together groups of coaxial transmission lines at different elevations so that a circulation of the fluid contained therewithin,

' whether air or other gas or fluid, may take place.

The lines are so grouped as to heat radiating capabilities and power carried that one group runs hotter than the other. Due to the convection principle a circulation of the contained fluid takes place.

The heat tends to mission'lines' 5, 6 and 1" having inner conductors The lower ends of the transmission 51; 61, 1|; linesmay beconsidered' as connected to a source of radio frequency energysuch as a transmitter while the upper ends may be'considered as con- -nected'to'a load or an antenna. In the showing of Figure 1', one transmission line has been labeled audio transmission line while the other pair have been labeled-video transmission line to indicate that the present invention may be adapted to a single-ended or unbalanced transmission line such as" maybe used for audio signals=and simultaneously, to apush-pull balanced transmissionline used for video signals in a television transmitting system. Of course, the present invention is not limited thereto but may be used wherever heavy current at high freguencies is being transmitted. The lower ends of each of the transmission lines are connected together by tubing 8 and the upper ends by tubing 9. In some cases, when the lines are sealed and subject to gas pressures above atmospheric, convection circulation may be naturally produced through the system especially if the unbalanced transmission line is arranged to run warmer than push-pull video transmission lines 6, I while r posed in the cross-connection tube 9 between the single and push-pull lines. However, since, transmission line 5 runs warmer than do lines 6 and 1, sufficient cooling may be obtained with the latter two lines connected in parallel as far as the air circulation is concerned. In operation, the heated air from transmission line 5 passes through the heat exchanger l2 and is cooled. The cool air then passes down through lines 6 and l, picking up heat from the inner conduc- Cooling fins may be provided 55 I tors 6|, H and is then forced through connections 8 back into transmission line 5, where it also picks up heat from conductor 5| before again entering heat exchanger l2.

While I have, in this figure, shown the heat exchanger as being air cooled with the circulation of the outer air through the heat exchanger aided by fan [3, it is within the scope of my invention to utilize a liquid cooled heat exchanger such as shown in Figure 2 of the drawing.

In Figure 2 I have shown a coaxial transmission line composed of outer conductor 25 and a hollow inner conductor 26. An insulating transformer oil may be passed through the hollow inner conductor 26. The oil connections 21 to the inner conductor from outside of the outer conductor 25 must be made of some insulating ma terial such as glass or an artificial rubber which is not affected by the cooling fluid. The cooling fluid is forced to circulate through the system by pump 30 though in some vertical installations thermo syphon circulation may be sufficient. The heat exchanger 32 in this figure is indicated as being of the water cooled type, water being allowed to flow in through an inlet 33 and out to waste at 34. The cooling fluid and the water are in contact with opposite sides of thin metallic separations. The separations may be arranged in sheet or tube form, as is well known. In some cases, suflicient cooling may be obtained without water cooling merely by substituting a radiator similar to the conventional automobile radiator or heat exchanger 32. In this case, convection may be relied upon to cause air to flow through the radiator.

While I have shown and particularly described several embodiments of my invention, it is to be distinctly understood that my invention is not limited thereto but that modifications Within the scope of my invention may be made.

I claim:

1. In combination, a plurality of substantially parallel transmission lines each having at least an outer shell, means for providing a fluid connection between said lines at each end thereof,

some of said lines having a heat radiating capacity exceeding that of the others and one end of said lines being at a higher elevation than the other whereby a circulation of fluid in said lines is caused.

2. In combination, a plurality of substantially parallel coaxial transmission lines, each having an inner conductor and an outer shell, means for providing a fluid connection between the outer shells of said lines at each end thereof, some of said lines having a heat radiating ca pacity exceeding that of the others and one end of said lines being at a higher elevation than the other whereby a circulation of fluid within said lines is caused.

3. In combination, a plurality of substantially parallel coaxial transmission lines, each having at least an outer shell, means for providing a fluid connection between said lines at each end thereof, said lines having their one ends at a substantially higher elevation than their other ends, at least all of said lines carrying sufficient radio frequency energy to cause excessive heating thereof and the outer shells of the remainder of said lines having a heat radiating capability in excess of that required to cool said remainder whereby convection causes a circulation from end to end of a fluid contained in said lines.

4. In combination, a plurality of substantially parallel coaxial transmission lines, each having an inner conductor and an outer shell, means for providing a fluid connection between said lines at each end thereof, said lines having their one ends at a substantially higher elevation than their other ends, at least some of said lines carrying suflicient radio frequency energy to cause excessive heating of the inner conductors thereof and the outer shells of the remainder of said lines having a heat radiating capability in excess of that required to cool said remainder whereby convection causes a circulation from end to end of a fluid contained in said lines.

GEORGE L. USSELMAN. 

